The present invention relates to a composite antenna apparatus.
As is well known in this technical field, various sorts of antenna apparatuses are presently mounted on vehicles. For instance, as these antenna apparatuses, antennas designed for SDARS (Satellite Digital Audio Radio Service), antennas designed for GPS (Global Positioning System), antennas designed for wireless telephone systems, antennas designed for AM/FM radios, and other antennas are proposed.
The SDARS (Satellite Digital Audio Radio Service) provides such services realized by a digital broadcasting system by utilizing satellites (will be referred to as “SDARS satellites” hereinafter) in The United States. That is, in The United States, It is developed and practically utilized a digital radio receiver capable of receiving digital broadcast programs by receiving either satellite waves or ground waves transmitted from the SDARS satellites. At the present stage, two broadcasting stations called as “XM” and “Sirius” provide 250, or more channels of radio programs in total so as to cover all states in The United States. Generally speaking, the above-described digital radio receivers are mounted on moving objects such as automobiles, and are capable of receiving electromagnetic waves in frequency bands of approximately 2.3 GHz to listen to digital ratio programs. In other words, digital radio receivers are such radio receivers capable of listening to mobile broadcasting programs. Since frequencies of received electromagnetic waves are present in approximately 2.3 GHz band, reception wavelengths at this time are approximately 128.3 mm. As to the above-described ground wave, after a satellite wave is once received by an earth station, a frequency of the received satellite wave is slightly shifted, and then, the satellite wave is re-transmitted based upon a linearly-polarized wave. In other words, the satellite wave corresponds to electromagnetic waves of a circularly-polarized wave, whereas the ground wave corresponds to electromagnetic waves of a linearly-polarized wave.
An XM satellite radio antenna apparatus receives electromagnetic waves of the circularly-polarized wave from two geostationary satellites, and also, receives electromagnetic waves of the linearly-polarized wave from ground linearly polarized wave facilities in an insensitive zone. On the other hand, a Sirius satellite radio antenna apparatus receives electromagnetic waves of the circularly-polarized wave from three earth orbiters, and also, receives electromagnetic waves of the linearly-polarized wave from ground linearly-polarized wave facilities in an insensitive zone.
As previously described, in digital radio broadcasting systems, since the electromagnetic waves having the frequencies of the approximately 2.3 GHz band are used, there are many cases that antenna apparatuses which receive these electromagnetic waves are set outdoors. As a consequence, in order that digital radio receivers are mounted on moving objects such as automobiles, antenna apparatuses of these digital radio receivers are mounted outside vehicle rooms, for instance, on roofs.
As SDARS antennas capable of receiving electromagnetic waves of the circularly-polarized wave, flat planar antennas such as patch antennas, and also, cylindrical type antennas such as helical antennas are used. Generally speaking, cylindrical type antennas may be popular, as compared with flat planar antennas. The reason why the cylindrical type antennas are more popular is that wide directivity may be achieved, since antennas are formed in cylindrical forms.
A description is made of helical antennas which constitute one of the cylindrical type antennas (refer to, Patent Document 1). While the helical antennas contain such a structure that at least one conducting wire is wound in a helix shape on a circumferential portion of a cylindrical member, the helical antennas can receive the above-explained electromagnetic waves of the circularly-polarized wave with higher efficiency. As a consequence, the helical antennas are employed in order solely to receive satellite waves. As materials of the cylindrical member, insulating materials such as plastic are used. Generally speaking, in order to improve reception sensitivities thereof, plural pieces (for instance, four pieces) of conducting wires are employed.
It is very difficult to wind plural pieces of conducting wires on a cylindrical member in a helix form. Under such a circumstance, the following helical antennas are proposed in Patent Document 2. That is, antenna patterns made of a plurality of conducting wires are printed on one face of an insulating film member having flexibility and provided with the antenna pattern. Then, this insulating film member provided with the antenna pattern is wound on a cylindrical member.
It should also be noted that in such a case that a helical antenna has a structure where a plurality of conducting wires are wound on a cylindrical member in a helix-shaped form, phases as to a plurality of satellite waves which are electromagnetic waves of circularly polarization mode are shifted from each other by a phase shifter in order that these shifted phases are made coincident with each other, while these plural satellite waves are received by plural pieces of these helix conducting wires of this helical antenna. After these satellite waves whose phases are coincident with each other are synthesized with each other, the synthesized satellite wave is amplified by a low noise amplifier (LNA), and then, the amplified satellite wave is transmitted to a main body of a receiver.
Another helical antenna is proposed in Patent Document 3. That is, in this helical antenna, both an antenna pattern constructed of four pieces of conductors and a phase shifter pattern electrically connected to the above-described antenna pattern are formed on one face of an insulating film member having flexibility and provided with antenna/phase shifter pattern.
On the other hand, as 3-wave commonly receivable antennas capable of receiving electromagnetic waves transmitted in a wireless telephone band, an FM radio band, and an AM radio band, rod antennas are known in this field. In any way, rod antennas are employed as wireless telephone-purpose antennas and AM/FM radio antennas. Rod antennas are constructed by winding electric wires on metal bodies, or glass fiber rods.
Furthermore, composite antennas capable of utilizing any of satellite communications and ground communications are proposed. For instance, a Patent Document 4 discloses a commonly receivable antenna constructed by arranging a monopole antenna on a substantially center axis within a dielectric cylinder which constructs a circularly polarization wave antenna. Also, a Patent Document 5 discloses such a composite antenna constituted by a four-line helical antenna and a monopole antenna. In this composite antenna, while four pieces of conductors are wound on a side face of a cylindrical dielectric body, a power supplying circuit is connected to the 4-line helical antenna, and supplies high frequency power to these four conductors in such a manner that phases of the high frequency power are sequentially different from each other by 90 degrees. The monopole antenna is provided on a substantially center axis of the cylindrical dielectric body.
On the other hand, GPS (Global Positioning System) is a satellite positioning system with employment of satellites. In the above-described GPS system, electromagnetic waves (GPS signals) are received which are transmitted from four GPS satellites among twenty-four GPS satellites which are orbiting the earth; a positional relationship between a moving object and the GPS satellites, and temporal errors are measured based upon the received electromagnetic waves; and then, a position and an altitude of the moving object on a map can be calculated based upon the principle of the trigonometrical survey.
The GPS system is utilized in car navigation systems and the like, which detect positions of traveling automobiles, and is widely popularized. A car navigation apparatus is arranged by a GPS antenna for receiving GPS signals; a processing apparatus for processing the GPS signals received by this GPS antenna so as to detect a present position of a vehicle; a display apparatus for displaying the present position detected by the processing apparatus on a map of a monitor; and the like. As the GPS antenna, a planar antenna such as a patch antenna is utilized.
Another composite antenna apparatus is proposed in which a planar antenna such as an SDARS antenna and a GPS antenna is mounted on a major face of an antenna base in addition to the above-described 3-wave commonly receivable antenna rod antenna capable of receiving electromagnetic waves transmitted in the portable wireless telephone band, the FM radio band, and the AM radio band (refer to, Patent Document 6).    [Patent Document 1] Japanese Patent Publication No. 2001-339227 A    [Patent Document 2] Japanese Patent Publication No. 2001-358525 A    [Patent Document 3] Japanese Patent Publication No. 2006-254049 A    [Patent Document 4] Japanese Patent Publication No. 10-290115 A    [Patent Document 5] Japanese Patent Publication No. 2002-314312 A    [Patent Document 6] Japanese Patent Publication No. 2008-61175A
As previously described, the Patent Document 4 and the Patent Document 5 disclose the composite antenna apparatuses constituted by two the antenna elements, namely, the helical antennas and the monopole antennas. In the composite antenna apparatuses having such structures, these two antenna elements are stored in the rod portion and the circuit board on which the electronic circuit such as the LNA circuit is mounted is stored in the base portion in order that the rod portion must be connected to the base portion in a mechanical manner and also an electric manner so that signals can be transmitted.
However, Patent Document 4 and Patent Document 5 neither disclose nor teach how to connect the rod portions with the base portions in the mechanical manners and electric manners so that signals can be transmitted.
Also, in such a case of the composite antenna apparatus arranged by the rod portions and the base portions, as previously explained, the signals are required to be transmitted between the rod portions and the base portions. In this case, normally, the following method may be employed. That is, while a first reception signal received by a helical antenna (first antenna element) is coupled with a second reception signal received by a monopole antenna (second antenna element) by a coupling device (coupler), the coupled signal is transmitted via a transmit path of a single line, and then, the coupled signal is separated into two original signals by a signal separator mounted on a circuit board. However, in such a signal transmit method, distribution losses (coupling/separating losses) may occur. As a result, there is such a problem that reception sensitivities measured in the respective elements of the composite antenna apparatuses are deteriorated.
In the composite antenna apparatus described in the above-mentioned Patent Document 6, two sets of the planar antennas are mounted on the major face of the antenna base. As a result, there is such a problem that if these two planar antennas are approximated to each other, then these planar antennas may interface with each other due to directivity thereof. In order to solve this interference problem, when the distance between these two planar antennas is increased, although the interference may be decreased, there is another problem that the resulting dimension of the composite antenna apparatus is increased.